探索和增强基于弛豫的钠 MRI 对比。

Exploring and enhancing relaxation-based sodium MRI contrast.

机构信息

Department of Biomedical Engineering, Faculty of Medicine and Dentistry, 1098 Research Transition Facility, University of Alberta, Edmonton, AB, T6G 2V2, Canada,

出版信息

MAGMA. 2014 Feb;27(1):21-33. doi: 10.1007/s10334-013-0390-7. Epub 2013 Jul 3.

DOI:10.1007/s10334-013-0390-7

PMID:23820724

Abstract

OBJECT

Sodium MRI is typically concerned with measuring tissue sodium concentration. This requires the minimization of relaxation weighting. However, (23)Na relaxation may itself be interesting to explore, given an underlying mechanism (i.e. the electric-quadrupole-moment-electric-field-gradient interaction) that differs from (1)H. A new sodium sequence was developed to enhance (23)Na relaxation contrast without decreasing signal-to-noise ratio.

MATERIALS AND METHODS

The new sequence, labeled Projection Acquisition in the steady-state with Coherent MAgNetization (PACMAN), uses gradient refocusing of transverse magnetization following readout, a short repetition time, and a long radiofrequency excitation pulse. It was developed using simulation, verified in model environments (saline and agar), and evaluated in the brain of three healthy adult volunteers.

RESULTS

Projection Acquisition in the steady-state with Coherent MAgNetization generates a large positive contrast-to-noise ratio (CNR) between saline and agar, matching simulation-based design. In addition to enhanced CNR between cerebral spinal fluid and brain tissue in vivo, PACMAN develops substantial contrast between gray and white matter. Further simulation shows that PACMAN has a ln(T 2f/T 1) contrast dependence (where T 2f is the fast component of (23)Na T 2), as well as residual quadrupole interaction dependence.

CONCLUSION

The relaxation dependence of PACMAN sodium MRI may provide contrast related to macromolecular tissue structure.

摘要

目的

钠磁共振成像通常关注于测量组织中的钠浓度。这需要最小化弛豫加权。然而，鉴于（23）Na 弛豫本身的潜在机制（即电四极矩-电场梯度相互作用）与（1）H 不同，因此探索其弛豫可能会很有趣。我们开发了一种新的钠序列，用于在不降低信噪比的情况下增强（23）Na 弛豫对比。

材料与方法

新序列被标记为稳态下的投影采集与相干磁化（PACMAN），它在读取后使用梯度重新聚焦横向磁化、短重复时间和长射频激发脉冲。它是通过模拟开发的，在模型环境（盐水和琼脂）中进行了验证，并在三名健康成年志愿者的大脑中进行了评估。

结果

稳态下的投影采集与相干磁化产生了盐水和琼脂之间大的正对比噪声比（CNR），与基于模拟的设计相匹配。除了在体内增强脑脊髓液和脑组织之间的 CNR 外，PACMAN 还在灰质和白质之间产生了显著的对比。进一步的模拟表明，PACMAN 具有 ln（T 2f/T 1）对比依赖性（其中 T 2f 是（23）Na T 2 的快速成分），以及剩余的四极相互作用依赖性。